Blaze of Multilayer Diffraction Gratings in the Soft X-Ray Range: Growth Design Taking into Account the Deformation of Groove Profiles

Abstract

It is shown that changing the angle of deposition of a coating onto a nanostructured substrate with an asymmetric profile (high-frequency blazed grating) has an effect both on smoothing of the groove profile of a multilayer grating (its symmetrization and/ or a decrease in its depth) and induces a significant displacement of the groove-profile maximum either to the left or to the right relative to the substrate profile. It is established that the displacement of interlayer boundaries is a linear function of the angle of deposition of the material and the change in the profile depth is a nonlinear function. By controlling the orientation of the source of the depositing material with respect to the groove’s working facet, controlled deformation of the profile can be attained in the nonlinear continuous growth equation. At a certain orientation of the source and taking into account realistic profile boundaries, the maximum diffraction efficiency of a grating at a given order of the spectrum is predicted to be higher than the similar efficiency of a grating with perfect triangular boundaries positioned strictly vertically one above the other. The optimal values of the boundary displacement, which are found from simulating the growth of a W/B4C 2500/mm grating with a blaze angle of 1.76° and an antiblaze angle of 20°, make it possible to achieve a diffraction efficiency of about 0.82−0.9 relative to the reflection of a multilayer mirror optimized for a wavelength of 1.3 nm. The maximum achievable efficiency for steeper angles of a non-working facet is somewhat higher.